U.S. patent application number 11/407801 was filed with the patent office on 2007-10-25 for mobile access node channel selection within a mesh network.
This patent application is currently assigned to Tropos Networks, Inc.. Invention is credited to Cyrus Behroozi, Amalavoyal Chari, Ramanagopal V. Vogety.
Application Number | 20070248044 11/407801 |
Document ID | / |
Family ID | 38619414 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070248044 |
Kind Code |
A1 |
Vogety; Ramanagopal V. ; et
al. |
October 25, 2007 |
Mobile access node channel selection within a mesh network
Abstract
An apparatus and method of a mobile node selecting a
transmission channel of a mesh network is disclosed. The method
includes the mobile node detecting a quality of routing beacons
received over a previously selected transmission channel. If the
quality of the routing beacons is below a predetermined threshold,
then the mobile node transmits probe requests on each of a
plurality of available transmission channels. Responses to the
probe request are collected from at least one upstream access nodes
over at least one of the available transmission channels. A new
transmission channel is selected based upon the responses received
over the available transmission channels.
Inventors: |
Vogety; Ramanagopal V.;
(Milpitas, CA) ; Behroozi; Cyrus; (Sunnyvale,
CA) ; Chari; Amalavoyal; (Sunnyvale, CA) |
Correspondence
Address: |
Tropos Patent Dept
PO Box 641867
San Jose
CA
95164-1867
US
|
Assignee: |
Tropos Networks, Inc.
|
Family ID: |
38619414 |
Appl. No.: |
11/407801 |
Filed: |
April 20, 2006 |
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 72/0406 20130101;
H04W 72/02 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04Q 7/00 20060101
H04Q007/00 |
Claims
1. A method of a mobile node transmission channel selection,
comprising: the mobile node detecting a quality of previously
selected routing path over a previously selected transmission
channel; if the quality of the routing path is below a
predetermined threshold, then the mobile node transmitting probe
requests on each of a plurality of available transmission channels;
collecting responses to the probe request from at least one
upstream access nodes over at least one of the available
transmission channels; selecting a new transmission channel based
upon the responses received over the available transmission
channels.
2. The method of claim 1, wherein the quality of the routing path
is determined by monitoring a percentage of routing beacons that
are successfully received over the previously selected transmission
channel.
3. The method of claim 1, wherein the previously selected
transmission channel is maintained if the quality of the routing
path is above the predetermined threshold.
4. The method of claim 1, wherein selecting a new transmission
channel based upon the response received over the available
transmission channels comprises: determining how many upstream
access nodes responded to the probe requests.
5. The method of claim 1, wherein selecting a new transmission
channel based upon the response received over the available
transmission channels comprises: measuring signal characteristics
of the responses to the probe requests.
6. The method of claim 5, wherein measuring the signal
characteristics of the responses includes determining a received
signal strength indicator.
7. The method of claim 5, wherein measuring the signal
characteristics of the responses includes determining an SNR of the
responses.
8. The method of claim 1, wherein the responses received from the
at least one upstream access node over the at least one available
transmission channel comprise a quality indicator of a routing path
to at least one gateway, wherein the at least one gateway
originates routing beacons.
9. The method of claim 8, wherein selecting a new transmission
channel further comprises comparing the quality indicator of each
path corresponding to each transmission channel of responding
upstream access nodes.
10. The method of claim 9, wherein the quality indicator of each
responding access node is based upon a persistence of routing
packets at the responding upstream access node.
11. The method of claim 1, wherein the probe request includes a
preferential information element that serves as a network
identifier that can influence selecting a new transmission
channel.
12. The method of claim 11, wherein the preferential information
element comprises a preference to select the new transmission
channel corresponding with a particular network identifier.
13. The method of claim 1, the available channels comprise 802.11
transmission channels.
14. The method of claim 1, wherein the mobile node comprises a
single radio that can transmit over multiple available transmission
channels.
15. The method of claim 1, wherein the mobile anode comprises
multiple radios and the channel selection is run by a second radio
while a first radio is transmitting and receiving data with an
upstream access node.
16. A method of selecting transmission channels through a mesh
network comprising mobile and fixed access nodes, comprising: a
plurality of gateways originating and broadcasting routing beacons,
each gateway broadcasting on one of a plurality of available
transmission frequencies; each mobile node detecting a quality of
routing beacons received over a previously selected available
transmission channel; if the quality of the routing beacons is
below a predetermined threshold, then the mobile node initiating
selection another of the plurality of available transmission
channels; the mobile node transmitting probe requests on each of
the available transmission channels; collecting responses to the
probe request from upstream access nodes over each of the available
transmission channels; selecting a new transmission channel based
upon the responses received over the available transmission
channels.
17. The method of claim 16, wherein the previously selected
transmission channel is maintained if the quality of the routing
beacons is above the predetermined threshold.
18. The method of claim 16, wherein selecting a new transmission
channel based upon the response received over the available
transmission channels comprises: determining how many upstream
access nodes responded to the probe requests.
19. The method of claim 16, wherein selecting a new transmission
channel based upon the response received over the available
transmission channels comprises: measuring signal characteristics
of the responses to the probe requests.
20. A method of a mobile node transmission channel selection,
comprising: the mobile node detecting a quality of routing beacons
received over a previously selected transmission channel; if the
quality of the routing beacons is below a predetermined threshold,
then the mobile node cycling between available transmission
channels, receiving and collecting beacons; selecting a new
transmission channel based upon the collected beacons received over
the available transmission channels.
21. The method of claim 20, wherein the beacons are 802.1
beacons.
22. The method of claim 20, wherein the beacons are mesh network
routing packets.
23. The method of claim 20, wherein the mobile node comprises a
single radio, and the mobile node cycles between transmission
channels while transmitted data packets over the previously
selected transmission channel.
24. The method of claim 20, wherein the mobile node comprises a
plurality of radios, and the mobile node cycles between
transmission channels of a first radio while transmitted data
packets with a second radio.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to wireless communications.
More particularly, the invention relates to a method and apparatus
of mobile access node transmission frequency selections for
wireless connections to clusters of mesh networks.
BACKGROUND OF THE INVENTION
[0002] Packet networking is a form of data communication in which
data packets are routed from a source device to a destination
device. Packets can be networked directly between a source node and
a destination node, or the packets can be relayed through a number
of intermediate nodes.
[0003] A wireless network can include a wireless device being
connected to a network through a base station that is wired to the
network. The wireless device can transmit data packets that are
received by the base station and then routed through the network.
The wireless network can include many base stations that are each
wired to the network.
[0004] FIG. 1 shows a prior art mesh network that includes a
gateway 110 connecting a client device 140 to a network (internet)
100 through fixed access nodes 120, 130. The connections between
the gateway 110 and the access nodes 120, 130 can be wireless.
Additionally, the connection between the access nodes 120, 130 and
the client 140 can be wireless. Wireless connections typically are
subject to conditions that can make the connections unreliable.
Such conditions include fading, multi-path and signal
interference.
[0005] Some mesh networks can additionally include mobile access
nodes that physically change their location over time. Mobile
access nodes add another layer of complexity because typically
optimal routes continually change for mobile access nodes.
Therefore, the routing selection for a mobile access node is more
complex than the routing selection for a fixed access node.
[0006] Mesh networks can additionally include multiple transmission
channels, in which access nodes must select the best transmission
channel. The changing physical location of mobile access nodes
typically requires the mobile access nodes to select the best
transmission channel. Transmission channel selection can be
required to be completed while the mobile access node is connected
to the mesh network.
[0007] It is desirable to have a wireless mesh network that
includes fixed and mobile access nodes. It is desirable that mobile
access nodes continually analyzes the quality of transmission links
and transmission frequencies of the mesh network, and select an
optimal transmission frequency from among all available
transmission frequencies.
SUMMARY OF THE INVENTION
[0008] One embodiment of the invention includes a method of an
access node selecting a transmission channel. The method includes
the mobile access node detecting a quality of routing beacons (or
quality of a routing path) received over a previously selected
transmission channel. If the quality of the routing beacons
(routing path) is below a predetermined threshold, then the mobile
node transmits probe requests on each of a plurality of available
transmission channels. Responses to the probe request are collected
from at least one upstream access node over at least one of the
available transmission channels. A new transmission channel is
selected based upon the responses received over the available
transmission channels.
[0009] Another embodiment of the invention includes a method of
selecting transmission channels through a mesh network, wherein the
mesh network includes mobile and fixed access nodes. The method
includes a plurality of gateways originating and broadcasting
routing beacons, each gateway broadcasting on one of a plurality
available transmission frequencies. Each mobile node detects a
quality of routing beacons received over a previously selected
available transmission channel. If the quality of the routing
beacons is below a predetermined threshold, then the mobile
transmits probe requests on each of the available transmission
channels. Responses to the probe request are collected from
upstream access nodes over each of the available transmission
channels. A new transmission channel is selected based upon the
responses received over the available transmission channels.
[0010] Other aspects and advantages of the present invention will
become apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a prior art mesh network.
[0012] FIG. 2 shows a wireless network that includes fixed access
nodes and mobile access nodes wirelessly connected to gateways, in
which each gateway forms a cluster having a specified transmission
frequency.
[0013] FIG. 3 is a flow chart that includes steps of one example of
a method of mobile node transmission channel selection.
[0014] FIG. 4 is a flow chart that includes steps of one other
example of a method of mobile node transmission channel
selection.
[0015] FIG. 5 shows a mesh network that includes several clusters,
in which the clusters include access nodes having routing paths to
gateways of the clusters.
[0016] FIG. 6 shows several clusters in which each cluster includes
multiple types of access nodes.
[0017] FIG. 7 is a flow chart showing an exemplary method of
selecting transmission channels through a mesh network.
DETAILED DESCRIPTION
[0018] As shown in the drawings for purposes of illustration, the
invention is embodied in an apparatus and method for mobile access
nodes analyzing a quality of available transmission frequencies of
a wireless network that includes fixed access nodes and mobile
access nodes, and selecting an optimal transmission frequency from
among all available transmission frequencies.
[0019] Mobile access nodes can be used to extend the coverage area
afforded by the fixed access nodes. In addition, mobile access
nodes can also provide network connectivity to client devices which
are either wireless-enabled or are directly plugged into an
Ethernet port on the mobile access node. Mobile access nodes can
connect wirelessly to the mesh network and join it through fixed or
mobile access nodes.
[0020] Fixed access nodes are typically mounted on streetlights,
utility poles, cable strands and the like. An embodiment of mobile
access nodes are designed to be mounted inside an automobile,
typically in the trunk, and drawing power from the battery of the
automobile. Fixed access nodes can connect together wirelessly to
form a mesh network that provides coverage to wireless client
devices such as laptops or PDAs equipped with wireless radios. A
fraction of the fixed access nodes can have provisioned backhaul
over fiber or Ethernet or WiMax or other point-to-point or
point-to-multipoint wireless backhaul.
[0021] FIG. 2 shows a wireless mesh network that includes fixed
access nodes and mobile access nodes. The wireless mesh network
includes gateways 220, 222. The gateways 220, 222 are connected to
a wired network 210. The gateways 220, 222 can be either wired or
wirelessly connected to the wired network 210. The wired network
210 can be connected to the internet 200. As will be described
later, the gateways originate routing beacons (packets) at a
predetermined rate, and at a predetermined transmission
frequency.
[0022] Clusters
[0023] Each of the gateways 220, 222 defines a cluster. A cluster
includes the corresponding gateway, and all access nodes connected
to the wired network 210 through the corresponding gateway. For
various reasons, it can be desirable for each cluster to operate
over a single, identified transmission frequency. For example, a
first cluster of the gateway 220 can have a pre-selected
transmission frequency of F1, and a second cluster of the gateway
222 can have a pre-selected transmission frequency of F2. The
single, identified transmission frequency can be different than the
transmission frequencies of other proximate clusters. This can be
desirable to minimize interference between proximate clusters.
Additionally, operating gateways and access node over a single
transmission frequency enables the gateways and access node to have
a single radio. For obvious reasons, a single radio access node is
less expensive than a multiple radio access node. If the wireless
connections between the gateways and access nodes of the mesh
network are operating according to the 802.11 protocol, each
cluster can be configured to operate on one of the available 802.11
transmission channels.
[0024] The mesh network further includes access nodes 230, 232,
234, 236, 238. The access nodes can include fixed access nodes 230,
234 and mobile access nodes 232, 236, 238. The fixed access nodes
230, 234 remain in a relatively stable location with respect to the
rest of the network. The mobile access nodes 232, 236, 238 can move
their locations with respect to the rest of the network. Each
access node, whether fixed or mobile, transmits at the frequency of
the cluster (as defined by gateways) that includes the access
node.
[0025] Clients 250, 252, 254 can be wired or wirelessly connected
to the access nodes 230, 232, 234, 236, 238. A shown in FIG. 2, a
first client 250 is wirelessly connected to the mobile access node
236, a second client 252 is wirelessly connected to the mobile
access node 232, and a third client 254 is wire connected to the
mobile access node 238.
[0026] Allowing mobile access nodes to move relative to the rest of
the mesh network requires the mesh network to be dynamic. The
transmission frequency selections and routing selections between
gateways and mobile access nodes should be continually monitored
and if needed, reselected. Additionally, mobile access nodes and
clients should be able to move within the network without the
clients being required to carry special hardware or software.
[0027] Single Radio Access Nodes
[0028] One implementation of the access nodes includes a single
radio. A single radio implementation is less expensive than a
multiple radio implementation of the access nodes, but also causes
some alternate and additional challenges not faced by a multiple
radio network. For example, a single radio implementation forces
time division multiplexed communication between the access nodes.
It is generally more difficult to monitor link quality and maintain
data transmission with a single radio.
[0029] Another advantage to operating different clusters at
different transmission frequencies is the minimization of
interference between access nodes of the mesh network.
[0030] Mobile Node Roaming
[0031] Assuming clusters of a mesh network each operate at
different transmission frequency, then a mobile access node that
roams from one cluster to a neighboring cluster should change its
transmission frequency to match the transmission frequency of the
cluster that offers the best wireless connection to a gateway. That
is, a mobile access node may be proximate to several different
clusters, but one of the clusters will typically provide the best
network connection. As the mobile access node moves, the cluster
offering the best network connection typically changes. Because the
different clusters can have different transmission frequencies, the
mobile access node must change its transmission frequency as
cluster the mobile access node is connected to changes. For
example, as the mobile access node 236 moves from being proximate
to the first cluster to being proximate to the second cluster, it
should desirably change its transmission frequency from F1 to F2.
Several factors, as will be described, can be used to evaluate the
quality of connection to each available cluster. Additionally,
implementing the mobile access node with a single radio adds
additional complexity to the monitoring and selecting of the
cluster, and corresponding transmission frequency.
[0032] New channel selection process desirably does not interfere
with an established network connection. That is, the mobile access
node may be connected and be communicating with the network while
roaming to a different cluster. Therefore, the channel selections
should be made with minimal interference with the network
connection. Again, if the mobile access node includes a single
radio, the selection is more complex.
[0033] FIG. 3 is a flow chart that includes steps of one example of
a method of mobile node transmission channel selection. A first
step 310 of the method includes the mobile node detecting a quality
of routing beacons received over a previously selected transmission
channel. This can be generalized as detecting a quality of a
routing path over a previously selected transmission channel. That
is, the path quality can be detected in other ways than by routing
beacon quality. If the quality of the routing beacons (routing
path) is below a predetermined threshold, then a second step 320
includes the mobile node selecting at least one of a plurality of
available transmission channels. A third step 330 includes the
mobile node transmitting probe requests on each of the available
transmission channels. A fourth step 340 includes collecting
responses to the probe request from upstream access node over each
of the available transmission channels. A fifth step 350 includes
selecting a new transmission channel based upon the responses
received over the available transmission channels.
[0034] The methods of transmission channel selection are described
with respect to mobile access node. However, the methods of
transmission channel selection can also be utilized by fixed access
nodes as well.
[0035] Routing Beacon Quality
[0036] Each gateway originates routing beacons (also referred to as
routing packets) which are used to select routing paths between the
gateway and each access node within the cluster defined by the
gateway. Each access node receives routing beacons from upstream
devices (the gateway or other access nodes) and selects an upstream
device depending upon the quality of the received beacons. Each
access node modifies and rebroadcasts the routing beacons of the
selected upstream devices. The mobile access nodes select routing
paths is essentially the same manner. That is, the mobile access
nodes select routing paths through a cluster based upon the quality
of the received routing beacons. An exemplary quality parameter
includes a persistence of the received routing beacons. That is,
the number of received routing beacons received over a period of
time.
[0037] If the quality (for example, persistence) of the received
routing beacons falls below a predetermined threshold, the mobile
access node can use this knowledge to check to determine whether
another cluster at a different transmission frequency provides a
better network connection. That is, as the mobile access node
moves, the network connection provided by a present cluster may
become inferior to a network connection provided by a neighboring
cluster. One way to detect this condition is to monitor the quality
of the routing beacons received from the present cluster at the
transmission frequency of the present cluster.
[0038] Selecting One of Available Transmission Channels
[0039] When the quality of the routing beacons falls below the
predetermined threshold, the mobile access node selects a different
transmission frequency to determine whether a different cluster
operating at a different transmission frequency may provide a
better network connection. Generally, there are only a finite
number of transmission channels available. The mobile access node
can tune to the available channels and test the quality of
available network connections. Based upon the tests, the mobile
access node can select a new transmission channel of a new cluster.
One embodiment includes the available channels being defined by the
802.11 protocol.
[0040] Mobile Node Transmitting Probe Requests
[0041] As previously mentioned, the testing of available channels
for a better network connection should take as little time as
possible to minimize the impact upon a connection of the mobile
access node to the network. An embodiment includes the mobile
access node transmitting probe requests over the available
transmission channels. One example of a specific embodiment
includes the probe requests defined by the IEEE 802.11 protocol.
That is, probe requests transmitted by clients and responded to by
access nodes are defined by the IEEE 802.11. These defined
processes can be enhanced with vendor specific information elements
included within the probe requests and probe responses.
[0042] All neighboring clusters that have transmission frequencies
included within the defined available transmission frequencies can
receive the probe requests.
[0043] Collecting Responses to the Probe Request
[0044] After the probe requests have been transmitted over the
available transmission frequencies, the mobile access node collects
all responses to the probe requests. All of the access nodes of the
clusters that receive the probe requests respond. The number of
responses and signal quality characteristics of the responses can
be monitored by the mobile access node. Based upon the number and
quality of the responses, a new transmission channel corresponding
with a particular new cluster can be selected.
[0045] The number of responses received can provide an indication
of how many of the probe requests were received by the cluster
corresponding with the transmission frequency of the probe request.
The number of responses can also provide an indication of how many
of the access nodes within the corresponding cluster received the
probe requests. Both of these factors can be helpful in deciding
which transmission frequency is selected.
[0046] The quality of the responses provides some indication of the
quality of the wireless connection of the mobile access node to the
cluster at the selected transmission frequency. This also can be
helpful in deciding which transmission frequency is selected. An
exemplary response quality that can be measured/monitored by the
mobile access node includes a receive signal strength indicators
(RSSI) which provides an indication of the signal strength of the
received response. Other embodiment include measuring the SNR
(signal to noise ratio) of the response. Other user defined
configurable preferences can additionally be included. For example,
mobile nodes can preferably route through fixed nodes rather than
mobile nodes, and therefore, preferably select a transmission
frequency of a fixed node over a transmission frequency of a mobile
node.
[0047] As will be described, other parameters can be used for
selecting a cluster and corresponding transmission frequency. For
example, the quality of routing paths within the clusters can be
additionally used to select a cluster and corresponding
transmission frequency. Each access node within a cluster has a
path quality that can be determined by the quality of routing
beacons received by the access node through the cluster from the
routing beacon originating gateway. This path quality provides an
indication of the quality of the path the mobile access node would
have if the mobile node was connected to the cluster through the
access node of the cluster. By knowing the path quality of the
connections to the corresponding gateways of the clusters having
the transmission frequencies being tested, the mobile access node
can make a more intelligent decision about which cluster the mobile
access node should connect to. That is, beyond the number of
responses received and the quality of the response, the path
quality of the connections to each available gateway can be used to
select the most desirable cluster and corresponding transmission
frequency.
[0048] Another embodiment includes other information parameters of
the response being used to influence selection of the new cluster.
For example, a client may preferentially select a network have a
particular network identifier.
[0049] Selecting a New Transmission Channel Based On the
Responses
[0050] Once the responses have been received, a new transmission
channel is selected. Many different combinations of the parameters
of the responses can be used in the selection. As described, the
selection can be based on the number of response and the signal
quality of the responses. Additionally, path qualities of the
connections to the gateways of the cluster can be used, and
preferences of access nodes of particular service providers can be
used, in the cluster and transmission frequency selection.
[0051] Selecting a New Transmission Frequency Based on Beacon
Reception
[0052] FIG. 4 is a flow chart showing steps of another method of a
mobile node transmission channel selection. A first step 410
includes the mobile node detecting a quality of routing beacons
received over a previously selected transmission channel. If the
quality of the routing beacons is below a predetermined threshold,
then a second step 420 is executed that includes the mobile node
cycling between available transmission channels, receiving and
collecting beacons transmitted by other clusters. A third step 430
includes selecting a new transmission channel based upon the
collected beacons received over the available transmission
channels.
[0053] The beacons are used to estimate a quality of a transmission
link between the transmitting access node and the mobile access
node. Examples of beacons that can be used include 802.11 beacons,
and routing beacons (packets) of a wireless mesh network as will be
described.
[0054] Embodiments of the access node can include single or
multiple radios. If the access node includes a single radio, then
the reception of beacons over other available transmission channels
from other clusters occurs through the single radio while the
single radio is also transmitting data packets. This can happen,
for example, by time multiplexing the data packet transmission with
the cycling between transmission channels. That is, the mobile
access node cycles between the transmission channels while
transmitted data packets over the previously selected transmission
channel. For multiple radio access nodes, the reception of beacons
over other available transmission channels can occur over a first
radio simultaneous with data packet transmission through a second
radio.
[0055] The received beacons are transmitted from neighboring
clusters. Therefore, the access node can monitor the quality of
network connections to cluster other than the cluster the access
node is presently connected to.
[0056] Routing Selections through Clusters
[0057] FIG. 5 shows a mesh network that includes several clusters,
in which the clusters include access nodes having routing paths to
gateways of the clusters. Each access node within each cluster
selects a routing path to the gateway within the cluster.
[0058] Access nodes 530, 532, 534, 536, 538, 540 (both fixed access
nodes and mobile access nodes) are coupled either directly or
indirectly to the gateways 520, 522, 524. That is, each access node
is either directly connected to an upstream gateway 520, 522, 524
or indirectly connected through another access node to at least one
of the upstream gateways 520, 522, 524. The decision of which
access nodes or gateways each access node is connected, can include
many factors. The network of FIG. 5 can include any number of
additional gateways and access nodes. As shown in FIG. 5, a client
550 can obtain access to the network by establishing a connection
to an available access node, such as, access node 536.
[0059] Gateways 520, 522, 524 broadcast routing packets (beacons),
which can be used to determine routing between access nodes 530-540
and gateways 520, 522, 524 of the network. The beacons are received
by all first-level access nodes (for example, fixed and mobile
access nodes 530, 532, 534), which are access nodes that are able
to receive gateway transmitted beacons, and directly route data
through to a gateway. For an exemplary embodiment, the beacons
originate at the gateways 520, 522, 524 at a predetermined rate.
For example, FIG. 5 depicts routing beacons being originated at the
gateway 520 at a rate of 4 routing beacons per second. The
first-level access nodes can measure the quality of the link
between them and the gateways by comparing the number of routing
beacons received over a period of time with the total number of
beacons transmitted over the period of time. For example, the
first-level access nodes can count the number of beacons received
over a ten second period. This number can be compared with the
number transmitted (40) over the ten second period to determine the
quality of the link between the first-level access node and the
transmitting gateway.
[0060] The beacons are used to establish a route from each access
node to a gateway. The first-level access nodes re-broadcast the
routing beacons, attaching their own information to the routing
beacons. The first-level access nodes maintain the routing beacon
transmission rate as determined by the gateways. That is, the
gateways transmit the routing beacons at a rate of four per second,
and the first-level access nodes re-broadcast the modified routing
beacons at the same rate at which routing beacons are successfully
received by the access nodes. This allows the second-level access
nodes to measure the path quality between them and the gateways.
The first level access nodes re-broadcast the beacons after adding
first level access node information, such as the address of the
first level access node. First level access nodes can be fixed
access nodes or mobile access nodes. It is to be understood that
there can be any number of mobile and fixed access nodes any number
of hops away from a gateway.
[0061] Mobile Access Node Routing Selections
[0062] Due to their mobility, the transmission links of mobile
access nodes are likely to change more rapidly than the
transmission links of fixed access nodes. Therefore, the quality of
selected routes (and non-selected routes) is likely to change more
rapidly than fixed access nodes. As a result, the routing
selections of the mobile access nodes should occur more often, and
place a greater weight on routing beacons most recently
received.
[0063] An example of how a mobile access node selects an upstream
routing path includes the mobile access nodes receiving routing
packets (routing beacons) from at least one upstream access node.
As described, the routing packets including information of at least
one upstream access node along a path to a gateway access node. The
mobile node assigns a weight to each received routing packet, in
which the weight is dependent on how recently the routing packet is
received. The mobile node calculates a packet success rate for each
upstream link by summing routing packets weights over a period of
time for each upstream link. The mobile node selects a routing path
through at least one upstream access node based upon the packet
success rate of routing packets received from each upstream access
node.
[0064] An additional packet success rate calculation can include
dividing the summed routing packet weight by a maximum possible
number possible for the sum.
[0065] The routing selections can be based at least in part upon
short and long routing packet success rates. For example, a short
test can be used to determine whether a link is alive. A long test
can include beacons received over a longer period of time, and aid
in the routing selections. For example, the short test can buffer
(receive and store) ten seconds worth of received routing beacons,
and a long test can buffer additional routing beacons for a total
time of 40 seconds. The maximum number of beacons that can be
received is set by the rate (for example, four routing beacons per
second) and the period of time of reception. For fixed nodes, a
routing selection typically includes counting the number of routing
packets received through each upstream link, and determining the
best link based on this number. As described, mobile access nodes
weight the routing beacons to additionally influence the routing
selections based upon when the beacons were received. Typically,
the mobile access nodes perform the long and short test more
frequently than the fixed access node because of their
mobility.
[0066] As will be described, mobile nodes prefers to select an
upstream route through a fixed access node, but will select an
upstream route through another mobile access node if the upstream
mobile access node has a link quality a predetermined amount
greater than the link quality of any fixed access node.
[0067] Due to the potential mobility of mobile access nodes, an
embodiment includes preventing fixed nodes from ever selecting a
link through an upstream mobile node. That is, fixed access nodes
only select links and routing paths through upstream fixed
nodes.
[0068] As previously described, the beacons are used to establish a
route from each access node to a gateway. The first level access
nodes re-broadcast the beacon data, attaching their own information
to the beacon. The information indicates to the second level access
nodes that the path to the gateway includes the first level access
node. As each access node rebroadcasts the beacons, each access
node adds additional information. The rebroadcast information can
include the addresses of all upstream access nodes along the path
to the gateway access node. That is, an embodiment includes each
access node that receives routing beacons, modifying the routing
beacons of a selected route by attaching an address of the access
node, and re-broadcasting the modified beacons. The address can be
an IP address of the access node or a MAC address of the access
node. Other information can include an indication that the routing
packet is being re-broadcast by a mobile access node, a current
packet success rate, or a reverse link success rate.
[0069] For one embodiment, the link quality of the beacon received
determines whether that beacon is rebroadcast by the access node.
If the quality of the beacon is the best of all received beacons,
it is rebroadcast. The beacons can be used to determine the quality
of the link in both an upstream (towards a gateway) direction, and
in a downstream (away from a gateway) direction. The upstream and
the downstream link qualities can be used by each access node to
select the best data routing path to a gateway. The link qualities
can be influenced by other wireless transmission factors such as
interference, noise and fading. Typically, the link qualities vary
more for mobile access nodes than for fixed access nodes. The link
qualities can be determined be calculating the percentage of
beacons that are transmitted and successfully received. The link
qualities can alternatively be determined by measuring a PER, BER
or SNR of received routing beacons.
[0070] The routing packets can be designated as beacons, and
include routing information. The beacons can be transmitted
according to an 802.11 protocol. Any of the access nodes are
operable as gateways as well.
[0071] If the mobile access node includes more than a single radio,
then one radio can be connected to the network while another radio
is determining routing beacon qualities of other available
transmission channels of other neighboring clusters. The
transmission frequency and cluster selection can occur in parallel
with the network connection. However, even with more than one
radio, the previously described methods of transmission channel
selection can be desirable due efficiency in the transmission
channel selection.
[0072] FIG. 6 shows several networks in which each network includes
multiple access nodes. For this embodiment, each network includes a
separate network identifier. A first network 610 includes a
transmission frequency of F1, a second network 620 includes a
transmission frequency of F2, and a third network 630 includes a
transmission frequency of F3. Access nodes within the networks 610,
620, 630 have been designated as an O, Y or X depending upon the
network identifier of the access node. A mobile access node 650
that is accessing one of the networks 610, 620, 630 over the
available transmission frequencies F1, F2, F3 can preferentially
select the network that includes a preferred network identifier.
The transmission channel selection can include measuring/monitoring
the number of response received from an access node of a network
having the preferred network identifier, the quality of the
responses received from the preferred access node, and the quality
of the paths of the access node to a gateway.
[0073] FIG. 7 is a flow chart showing an exemplary method of
selecting transmission channels through a mesh network, wherein the
mesh network includes mobile and fixed access nodes. A first step
710 includes a plurality of gateways originating and broadcasting
routing beacons, each gateway broadcasting on one of a plurality
available transmission frequencies. A second step 720 includes each
mobile node detecting a quality of routing beacons received over a
previously selected available transmission channel. If the quality
of the routing beacons is below a predetermined threshold, then a
third step 730 includes the mobile node transmitting probe requests
on each of the available transmission channels. A fourth step 740
includes collecting responses to the probe request from upstream
access nodes over each of the available transmission channels. A
fifth step 750 includes selecting a new transmission channel based
upon the responses received over the available transmission
channels.
[0074] The methods of selecting transmission frequencies can be
implemented as software operating on a mobile access node. The
software programably operates the mobile access node to select a
transmission frequency as has been described.
[0075] Although specific embodiments of the invention have been
described and illustrated, the invention is not to be limited to
the specific forms or arrangements of parts so described and
illustrated. The invention is limited only by the appended
claims.
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